1. Field of the Invention
The present invention relates generally to microelectromechanical systems, and particularly to a method of fabricating a microelectromechanical system.
2. Technical Background
Micromechanical actuators are essential for microelectromechanical systems (MEMS) that require moveable components. One process commonly used to fabricate MEMS is surface micromachining. Surface micromachining involves the deposition and patterning of semiconductor thin films. An example of such a process entails the deposition of three structural thin film layers of polycrystalline silicon and two sacrificial layers of silicon dioxide. While this process allows a great deal of flexibility in device design, it has certain drawbacks.
One major drawback of this technique is its inability to yield tall structures such as high quality mirrors. Mirrors fabricated by this process are currently produced as horizontal, planar thin films. They are then rotated 90xc2x0 by hand to form vertical structures at right angles to the substrate. This task is time-consuming, difficult, and reduces yield due to breakage. Further, the assembled mirrors are often warped due to geometry and film stresses. The mirrors may also require release holes in the surface after initial formation to permit etching of certain sacrificial layers located thereunder.
On the other hand, a known method of making tall structures is referred to in the art as LIGA. This method involves lithography, electrodeposition (i.e., galvanoforming), and molding. According to this method, optical or x-ray lithography is used to define patterns in polymer resist films such as polymethyl methacrylate (PMMA). The patterns are then filled with metal by electrodeposition.
While this method permits the formation of relatively large structures with high aspect ratios (tens or hundreds of microns tall and only a few microns thick), it also has certain drawbacks. One drawback is that this method does not allow the device complexity or freedom of motion obtained by surface micromachining.
In view of the foregoing, it would be desirable to provide a method of fabricating MEMS devices with the complex features of surface micromachining and the high aspect ratios of LIGA.
The above and other objects are provided by the following method. First, an insulating layer is deposited on a substrate. Next, a base in the form of a first conducting layer is deposited on the insulating layer and is patterned. A first sacrificial layer is then deposited on the first conducting layer and patterned. A slider in the form of a second conducting layer is then deposited on the first sacrificial layer and patterned. A second sacrificial layer is then deposited on the second conducting layer and patterned. Next, a retainer in the form of a third conducting layer is deposited on the second sacrificial layer and patterned. A mask is then deposited on the third conducting layer and patterned. Next, a reflector in the form of a fourth layer is deposited through the mask onto the third conducting layer. Finally, the mask, first sacrificial layer and second sacrificial layer are removed.